We have, in previous studies, made a discovery that generalized transducing Salmonella phage recombine with various unrelated bacteriophages to evolve into new hybrid phage species. Recently, we isolated an unusual Salmonella typhimurium-E. coli hybrid with sensitivity to coliphage lambda and Salmonella phage P22. This bacterial strain and its derivatives have facilitated construction of new hybrid phage species between the evolutionary diverse phage lambda, which has a unique genome, and phage P22 which has a circularly permuted genome. Similarly hybrids between phi80 and P22 phages were isolated. These hybrid phages provide an excellent model for studying a mechanism of genetic evolution, control of gene expression within gene clusters derived from diverse phages, phage morphogenesis, chromosome structure and nature of transduction. To understand the above mechanisms, we propose to study the follwing: (1) Regulation of the lambda late genes by the P22 early genes in lambda-P22 phage replication; (2) Isolation of repressor molecules of P22 and lambda, their in vitro binding to P22-lambda and lambda-P22 DNAs, and effects on in vitro transcription; (3) Physical mapping of lambda-P22 by using an E. coli restriction enzyme. (4) Genetic mapping of phi80-P22 and P22-phi80 hybrid phages; (5) Heteroduplex studies of phi80-P22 hybrid phage DNA with phi80 DNA and (6) Isolation of hybrid between P22 and Mu-1 phages. BIBLIOGRAPHIC REFERENCES: Yamamoto, N. An unusual strain of bacteriophage P221 carries the P22 tail gene. Symposia on Viral Morphogenesis, Proceedings of the International Association of Microbiological Society. Vol. 2, 177-179, 1975. Sato, M., Tanaka, H., Yamada, T. and Yamamoto, N. Virus induction from cell cultures persistently infected with rubella virus. Symposia on Persistent and Slow Infections. Proceedings of the International Association of Microbiological Society. Vol. 3, 153-157, 1975.